A Digital Lock-In Amplifier Assisted Active Islanding Detection Technique for DC Microgrids

Abstract

Islanding detection is crucial in both AC and DC grids, failure of which might result in unstable operating points. This is a key impediment to increase renewable energy integration. Islanding detection in the DC grid is relatively a new concept as compared to AC grid islanding. In the DC grid, islanding detection majorly depends upon threshold settings with respect to under/over voltage limits (which fail during zero power mismatch (ZPM) conditions). Some active islanding techniques focus on disturbance injection, but the larger disturbance in those techniques causes unstable operations in the grid. This research proposes an impedance-based active islanding detection scheme to address the shortcomings of existing techniques. The digital Lock-In Amplifier (D-LIA) and sensors in PV are used to accomplish the approach. The proposed scheme can detect islanding during the ZPM scenario without any degradation of power quality. This scheme can discriminate islanding conditions efficiently with a disturbance injection of lower magnitude. The proposed active islanding detection technique is modeled in MATLAB/Simulink, with experimental validation on a DC Microgrids hardware test bed with the dSPACE (DSP-1104) controller.